The increased use and reliance on microprocessor control systems for automotive vehicles and increased confidence in hydraulic as opposed to mechanical systems is making substantial progress in engine systems design possible. Electrohydraulic systems in vehicles provide more flexibility to increase engine performance, with a drawback that now more systems will need a source of pressurized hydraulic fluid to operate. These separate systems can take up much room and add weight as well as creating parasitic losses. This is especially true for those systems which only occasionally require pressurized hydraulic fluid.
One such electrohydraulic system is a control for engine intake and exhaust valves. The enhancement of engine performance to be attained by being able to vary the acceleration, velocity and travel time of the intake and exhaust valve in an engine is well known and appreciated in the art. This allows one to account for various engine operating conditions through independent control of each valve to optimize engine performance. This type of system typically requires a constant supply of pressurized hydraulic fluid to operate.
Another type of electrohydraulic system provides hydraulic assist to a turbocharger to improve the response time of the turbocharger under certain engine operating conditions. At low engine operating speeds and during increasing load conditions, the effectiveness of a turbocharger as a means to quickly boost the engine air supply is rather low. Only after some initial increase in engine speed and power has already been achieved, does the turbocharger become an effective means for further increase in engine power. Adding a hydraulic turbine wheel to the turbocharger can substantially alleviate this problem. Such a turbine, which can be selectively activated by supplying it with pressurized oil for brief periods during which the energy supplied by the exhaust gas is too low, can significantly improve the response of the engine/turbocharger system. The problem with adding a hydraulic turbine to a turbocharger is that it also requires installation of a high pressure hydraulic system, which adds additional cost and complexity to the vehicle. This is especially true because this hydraulic system would only be needed occasionally.
In an engine where a hydraulic system already exists, such as one having an electrohydraulic valvetrain, modifying the hydraulic system to perform as a dual purpose system providing boost to the turbocharger can save cost, space and weight as well as reducing the parasitic losses.